Long-Span Prestressed Concrete Box Girder Research Articles

Analysis on the causes of cracking and excessive deflection of long span box girder bridges based on space frame lattice models

Long-span prestressed concrete box girder bridges (continuous girder and rigid frame bridges) tend to have some apparent diseases. On the one hand, cracks in various directions appear in different positions of different slabs of the box girder; on the other hand, the deflection of the structure develops for a long time, which significantly exceeds the design expectation eventually. This paper intends to use the space frame lattice model, combined with the complete stress index system, to analyze the causes of cracks in different forms in an actual bridge. Unlike the single beam model and the transverse frame model under the guidance of the existing code system, the space frame lattice model that discretizes an entire box girder section into individual slabs can more precisely simulate the load that exceeds the code but exists. In addition, the complete stress index system enriches the design of box girder bridges and can well explain the cracking causes of old bridges. This paper also discusses the effect of the difference in creep and shrinkage caused by the difference in thickness among slabs on the deflection.

Life-Cycle Monitoring of Long-Span PSC Box Girder Bridges through Distributed Sensor Network: Strategies, Methods, and Applications

Structural health monitoring (SHM) has attracted much attention in recent years, which enables early warnings of structural failure, condition assessments, and rational maintenance/repair strategies. In the context of bridges, many long-span steel bridges in China have been installed with the SHM systems; however, the applications of the SHM in prestressed concrete (PSC) bridges are still rather limited. On the other hand, the PSC box girder bridges are extensively used in highway and railway systems and premature damage of these bridges is often reported, resulting in considerable maintenance and/or replacement costs. First, this paper presents a state-of-art review on the SHM of long-span PSC bridges. Monitoring strategies, methods, and previous applications for these bridges are summarized and discussed. In order to well capture the behavior of the bridge during its whole life and to maximize the use of sensors, a life-cycle monitoring strategy is proposed, in which the sensor layout is determined according to requirements for construction monitoring, completion test, and in-service monitoring. A case study is made on a three-span PSC box girder bridge in China. The system configuration, sensor layout, and data communications, and so forth, are presented. The up-to-date monitored structural responses are analyzed and compared with the design values.

Quantitative Design of Backup Prestressing Tendons for Long-Span Prestressed Concrete Box Girder Bridges

Excessive deflections unexpected at the midspan have commonly appeared in long-span prestressed concrete box girder bridges, mainly because of the high degree of uncertainty in concrete creep and shrinkage, prestress loss, and variations in the environment. Arrangement of backup prestressing tendons that will be tensioned based on deflection development during the service years is an effective solution to this problem. First, an uncertainty analysis of the long-term deformation at the midspan of a bridge was performed using the Latin hypercube sampling method, with the consideration of model uncertainty of creep and shrinkage and random properties of influencing factors; consequently, the 95% confidence interval of the deformation at the midspan was determined. Then, a quantitative design of backup tendons was performed on the basis of the difference between the lower limit and mean value of the 95% confidence interval of deformation. Lastly, the efficiencies of different arrangement schemes of backup tendons were compared, and results show that arrangement of combined external tendons along the girder is the most effective measure for control of long-term deflection.

Experimental analysis of the effective pre-stress in large-span bridge box girders after 40 years of service life

The rheological properties of concrete and pre-stressing steel have a significant influence on the deformation and pre-stress losses of p.c. members and thus affect their long-term deflection and service behaviour. Long-span concrete bridge girders can be particularly sensitive to pre-stress losses as the dead load is large compared to the total load. Some observations of excessive long-term deflections have been made of long-span pre-stressed concrete box girder bridges over the last few years. This has led some researchers to question the reliability of the available theoretical models to provide correct long-term predictions. The main results of experimental tests conducted on 9 concrete bridge box-girders with a span of 35m are presented in this work. The girders, which were part of an Italian motorway bridge dismantled after 40years of service life, were tested up to failure with a specially built test frame. The mean deformation measured over five zones of each beam allowed the effective stress in the pre-stressing tendons to be evaluated for a total of 45 zones. Finally, the experimental data have been compared with theoretical predictions obtained by applying both the rules of an international standard (Eurocode 2) and a refined analytical model that takes into account the presence of two types of concrete with different properties as well as the various stages of the construction and pre-stressing.

Cracking Control for Diaphragm of Long-Span Prestressed Concrete Box Girder Bridge at the Early Age

This paper presents the results of a study on the early-age cracking behavior of diaphragm in long-span prestressed concrete box girder bridge with cracking control techniques. Based on the three-dimensional hydration heat temperature conduction and humidity diffusion theory, and according to the similarity of differential equation between the humidity diffusion theory and temperature conduction theory, the early-age cracking of diaphragm was simulated by a three-dimensional finite element model with consideration of concrete shrinkage, creep, cement hydration heat and variation of temperature. The numerical simulation accurately predicts the cracking region and size and stress time history of diaphragm, and provides load standard for cracking control techniques of prestressing force. The cracking control techniques of prestressing force effectively avoid the early-age cracking of diaphragm by application of practical engineering.

Comparative Study on Seismic Performance of Prestressed Concrete Box-Girder Bridges with Corrugated Steel Webs

Prestressed concrete (PC) box-girders with corrugated steel webs are one of the promising steel concrete composite structures applied to highway bridges. Although the basic structural characteristics including bending, shearing and torsion, etc., have been paid much attention, few researches on the seismic performance of this type of bridges are found, especially when the span of this type of bridges becomes larger and larger. In this paper, the seismic performance of one long-span PC box-girder bridge with corrugated steel webs is studied and compared with a conventional box-girder bridge with concrete webs, based on response spectrum analysis using ANSYS. The results show that, the vertical and transverse displacements of the box-girder with corrugated steel webs are slightly less than those of the box-girder with concrete webs, but the longitudinal displacement reverses, under the same earthquake excitation. The bending moments of representative sections of the box-girder bridge with corrugated steel webs are only about 70% ~ 90% of those of the corresponding conventional PC girder bridge. The results indicate that the box-girder bridge will have better seismic performance if the corrugated steel webs are adopted instead of the concrete webs, but it could also fulfill the tasks such as displacement control which resulted from stiffness reduction.

Effect of Pier Vertical Deformations on Deflections of Main Girders for High Pier and Long-Span Continuous Rigid-Frame Bridges

In some long-span prestressed concrete box girder bridges, excessive deflections of main girders are often observed. These unacceptable deflections have detrimental influence on the serviceability and safety of the structures. To better understand and estimate short term and long term deflections for prestressed concrete box girder bridges, pier vertical deformation and its effect on deflections of main girders of Jinghe Bridg is investigated in this paper. Piers in Jinghe Bridge are tall and the difference in height between piers up to 22 m. Analysis indicates that although the short term deformations of piers are small, the long term deformations of piers can be 3 times as large as that of short-term ones. The maximum short-term downward deflection of Jinghe Bridge caused by pier deformation for main girders is 7.7 mm and the maximum long-term downward deflection is 33.3 mm. These values are relatively small compared with the span length of the bridge. But when the deflection of the main girder itself is also included, the final total deflection of the main girder may exceed the design code limit.